WO 2008/131735 A1 discloses a light emitting diode chip wherein a first and second electrical connection layer are arranged at a rear side of the light emitting diode chip, the rear side lying opposite the radiation exit area, and are electrically insulated from one another by a separating layer, wherein a partial region of the second electrical connection layer extends from the rear side through a perforation of the active layer in the direction toward the front side of the light emitting diode chip. Such a contact-connection of a semiconductor chip has the advantage that the radiation exit area can be free of contact areas and, consequently, the emitted radiation is not shaded.
The light emitting diode chip is a so-called “thin-film” light emitting diode chip, wherein the original growth substrate of the semiconductor layer sequence is detached and, instead, the semiconductor layer sequence is connected at a side lying opposite the original growth substrate to a carrier by a solder layer. In the case of a thin-film light emitting diode chip of this type, it is advantageous if that side of the semiconductor layer sequence which faces the carrier is provided with a mirror layer to deflect radiation emitted in the direction of the carrier in the direction of the radiation exit area and thereby increase radiation efficiency.
For the visible spectral range, silver, in particular, is suitable as a material for the mirror layer. However, in the case of a mirror layer composed of silver, it is difficult to obtain both good adhesion on the semiconductor material, a good electrical connection to the semiconductor material, high reflection and reliable protection against corrosion or migration of the silver into adjacent layers.
An adhesion promoter layer can be inserted between the semiconductor surface and the mirror layer to improve adhesion of a mirror layer composed of silver on a semiconductor material. However, reflectivity is generally reduced by such an adhesion promoter layer between the semiconductor material and the mirror layer. Such an adhesion promoter layer should therefore generally be applied in a very thin fashion, whereby process control is made more difficult.
It could therefore be helpful to provide a light emitting diode chip comprising a rear-side mirror layer wherein the mirror layer is distinguished, in particular, by good adhesion on the semiconductor material, good electrical connection to the semiconductor material, high reflection and protection against corrosion and degradation or migration of the silver into adjacent layers.